Child coordinators notify their parent upon -start and -stop.

ios/clean/chrome/browser/browser_coordinator.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // ======                        New Architecture                         =====
 // =         This code is only used in the new iOS Chrome architecture.       =
 // ============================================================================
 
 #ifndef IOS_CLEAN_CHROME_BROWSER_BROWSER_COORDINATOR_H_
 #define IOS_CLEAN_CHROME_BROWSER_BROWSER_COORDINATOR_H_
@@ skipping 12 matching lines @@
 
 // The context object for this coordinator.
 @property(nonatomic, strong, readonly) CoordinatorContext* context;
 
 // The browser object used by this coordinator and passed into any child
 // coordinators added to it. This is a weak pointer, and setting this property
 // doesn't transfer ownership of the browser.
 @property(nonatomic, assign) Browser* browser;
 
 // The basic lifecycle methods for coordinators are -start and -stop. These
-// are blank template methods; child classes are expected to implement them and
-// do not need to invoke the superclass methods.
+// implementations only notify the parent coordinator when this coordinator did
+// start and will stop. Child classes are expected to override and call the
+// superclass method at the end of -start and at the beginning of -stop.
+
 // Starts the user interaction managed by the receiver. Typical implementations
 // will create a view controller and then use |baseViewController| to present
-// it.
-- (void)start;
+// it. This method needs to be called at the end of the overriding
+// implementation.
+- (void)start NS_REQUIRES_SUPER;
 
-// Stops the user interaction managed by the receiver.
-- (void)stop;
+// Stops the user interaction managed by the receiver. This method needs to be
+// called at the end of the overriding implementation.

[rohitrao (ping after 24h), 2017/03/08 13:01:03]

Called at the beginning, not the end?

[lpromero, 2017/03/08 13:45:41]

Done.

+- (void)stop NS_REQUIRES_SUPER;
 
 @end
 
 #endif  // IOS_CLEAN_CHROME_BROWSER_BROWSER_COORDINATOR_H_